The present invention relates to techniques for preventing counter-flow in a pilot-type channel valve. More particularly, an objective of the present invention is to realize a pilot-type channel valve providing counter-flow prevention that can be driven with a small amount of power, that resists freezing, and that provides a superior valve-opening response.
Pilot-type channel solenoid valves are well known and an example is described in Japanese Utility Model Laid-open Publication No. 59-83262. This art will be explained with reference to FIG. 1. In FIG. 1, reference number 1 indicates a body. An inlet 2 and an outlet 3 are formed on this body 1. Inlet 2 and outlet 3 are connected to each other via a passage 4. A valve seat 5 is formed on the top end face of passage 4. A cylindrical main valve 6 having a bottom is vertically movably disposed inside body 1. A ring-shaped protrusion 9 is integrally provided on the external bottom surface of main valve 6. Tube-shaped protrusion 9 can contact or separate from valve seat 5. A pilot chamber 7 is formed inside main valve 6. A pilot hole 8 is defined in the center of the bottom of main valve 6. A solenoid coil 10 is provided on the upper edge of body 1. A plunger 11 and a spring 13 are provided inside solenoid coil 10. A spherical pilot valve 12 is installed at the tip of plunger 11. When no electrical power is applied to solenoid coil 10, pilot valve 12 is biased by spring 13 and closes pilot hole 8. When electrical power is applied to solenoid coil 10, the magnetic force causes pilot valve 12 to separate from pilot hole 8. An extremely narrow gap 14 is provided between the external perimeter of main valve 6 and the internal perimeter of body 1.
According to this pilot-type channel solenoid valve, even when a large pressure difference exists between inlet 2 and outlet 3, main valve 6 can be opened by applying a small magnetic force to pilot valve 12. When a small magnetic force is applied to pilot valve 12, the high pressure within pilot chamber 7 is released through pilot hole 8, and therefore the high pressure, which is being applied to inlet 2, opens main valve 6. Even when a high pressure is being applied to inlet 2, the electromagnetic force required to open the valve can be small. When no electrical power is being applied to solenoid coil 10, the high pressure being applied to inlet 2 works in the direction of closing main valve 6; as a result, no electromagnetic force is needed to maintain the closed valve state. Therefore, a pilot-type channel solenoid valve, even when used in a pipe that is subject to a large pressure difference between inlet 2 and outlet 3, provides advantages in that solenoid coil 10, which is used for controlling the opening and closing of the channel, can be made compact and the valve can be driven with a small amount of electric power.
In an ordinary pipe, the direction of the fluid flow is predefined in that the fluid enters through inlet 2 and exits through outlet 3; therefore, no particular problems are encountered by a pilot-type channel valve. However, a pilot-type channel valve is characterized in that it has an inability to prevent counter-flow. If high pressure is applied from the side of outlet 3 against a closed pilot-type channel valve, the valve will easily open. Given that a pilot-type channel valve cannot prevent counter-flow, Japanese Utility Model Laid-open Publication No. 59-83262 proposed means for preventing the channel valve from generating abnormal noise during counter-flow.
A first means for preventing counter-flow in a channel valve is increasing the spring force that biases the movable valve toward the closed position. Therefore, in order to prevent counter-flow in a channel valve, it is necessary to use a channel valve that is closed by means of a large spring force and is opened using a large amount of power, instead of using a pilot-type channel valve. A second means is inserting a counter-flow prevention valve into the pipe and downstream from the pilot-type channel valve. Japanese Patent Laid-open Publication No. 10-2445 describes a technique of incorporating a counter-flow prevention valve inside a pipe that is connected to a channel valve, and this technique is intended to be applicable to pilot-type channel valves.
However, the first means, i.e., a channel valve that is closed by means of a large spring force and is opened by applying a large amount of power in order to open and close the channel while preventing counter-flow, requires a large amount of power for opening and closing the channel, thereby increasing the size of the channel valve. That is, the advantage of a pilot-type channel valve, which is the ability to be driven by a small amount of power, cannot be attained. The second means, i.e., a method of inserting a counter-flow prevention valve within the pipe downstream from a pilot-type channel valve, does not present the above-noted problem. However, this method still faces a problem in that the counter-flow prevention valve cannot recover from freezing once it becomes inoperable due to freezing. When the fluid that flows through the channel is a gas, the gas flows through the channel while being compressed or expanded, resulting in gas temperature fluctuations. If the pilot-type channel valve opens and the gas flows downstream while undergoing adiabatic expansion, the gas temperature will decrease; as a result, low-temperature gas will pass through the counter-flow prevention valve. If the gas contains water vapor, this water vapor may freeze within the counter-flow prevention valve. In this case, if a counter-flow phenomenon occurs after the pilot-type channel valve has closed, the counter-flow prevention valve, which is intended to prevent a counter-flow, becomes frozen in the open position and cannot prevent counter-flow. Also, it is not possible to heat the counter-flow prevention valve to prevent it from freezing when the gas, which has been cooled by undergoing adiabatic expansion, is passing through this counter-flow prevention valve; as a result, the valve tends to freeze. Moreover, the method of inserting a counter-flow prevention valve within the pipe downstream from a pilot-type channel valve also has a problem of poor valve-opening response. According to this method, opening the pilot-type channel valve increases the pressure within the pipe between the pilot-type channel valve and the counter-flow prevention valve, and the counter-flow prevention valve opens when this pressure reaches a predetermined value. In the method of inserting a counter-flow prevention valve in the downstream pipe, it takes time for the pressure to rise, because the capacity of the pipe between the pilot-type channel valve and the counter-flow prevention valve is large. The objective of the present invention is to create a valve that can prevent counter-flow, that can enjoy the advantage of a pilot-type channel valve, which is the ability to be driven by a small amount of power, that can prevent freezing of the counter-flow prevention valve, that can recover from freezing in the event that freezing occurs, and that also has an excellent valve-opening response.
In the pilot-type channel valve according to the present invention, a counter-flow prevention valve is disposed within the body of the pilot-type channel valve. When a counter-flow prevention valve is disposed within the body of the pilot-type channel valve, while electrical power is applied to the solenoid coil and the pilot-type channel valve is open, or while a high-pressure working fluid is introduced and the pilot-type channel valve is open, i.e., while a gas is flowing through the counter-flow prevention valve while undergoing adiabatic expansion, the heat generated by the application of the electrical power to the solenoid coil or the heat generated by the introduction of the working fluid is conducted through the body and is efficiently transferred to the counter-flow prevention valve. Therefore, even if the gas flowing in the channel contains water vapor and even when this gas cools due to significant expansion, the water vapor can be prevented from freezing within the counter-flow prevention valve. Moreover, even if freezing should occur for some reason, the heat from the solenoid coil or the heat generated by the adiabatic compression of the working fluid is conducted through the body and is efficiently transferred to the counter-flow prevention valve, thereby quickly thawing the frozen area. Furthermore, because the counter-flow prevention valve is disposed within the body of the pilot-type channel valve, the pipe volume between the pilot-type channel valve and the counter-flow prevention valve is small. Consequently, the pressure within the pipe rises quickly, thereby opening the counter-flow prevention valve without delay. Therefore, in order to provide a structure for opening and closing a channel while preventing counter-flow, the valve of the present invention can be used to achieve desirable characteristics, i.e., the counter-flow prevention valve is resistant to freezing and the valve itself has an excellent valve-opening response, particularly for a pipe that supplies hydrogen to fuel cells, which has been gaining much attention in recent years, while enjoying the advantage of a pilot-type channel valve, which is the ability to be driven by a small amount of power. A pilot-type channel valve providing counter-flow prevention according to the present invention is extremely useful for a hydrogen-supply pipe, because water vapor is mixed within such a pipe and because hydrogen passes through the pipe while undergoing volume changes. Note that in the case of the present invention, its advantages, i.e., the ability to be driven by a small amount of power, the resistance to freezing, and the excellent valve-opening response, can be enjoyed even if the counter-flow prevention valve is inserted on the upstream side of a pilot-type channel valve.